The present invention relates to a method for cutting (or machining) a honeycomb core.
Honeycomb sandwich panels using fiber-reinforced composites (prepregs) are light in weight and high in strength, so that they have been widely used for automobiles, ships, aircrafts, etc. The honeycomb sandwich panels are generally produced by placing an assembly composed of a couple of skins made of a fiber-reinforced composite and a honeycomb core covered therewith on a forming tool, and by heating the assembly under a pressure to form it into a desired shape. An adhesive may be provided between the honeycomb core and the skins. The honeycomb core comprises a plurality of hollow tubular cells made of a fiber, etc., and appropriately cut into a desired shape beforehand. In general, at the edges of the honeycomb core is provided a tapered portion to prevent the edges from being deformed or crushed during the heating under a pressure.
Conventionally, the honeycomb core has been cut by a method comprising the steps of: fixing the honeycomb core on a workbench by a double faced adhesive tape; cutting the honeycomb core by a cutter; and finishing the cut surface by a sand paper. However, this method often results in poor form accuracy of the cut surface. The hollow tubular cells of the honeycomb core is not sufficient in hardness and strength, whereby the hollow tubular cells are pushed down and bent by the cutting part of the cutter. Thus, the cell walls in the cut surface result in inappropriate deformation such as crumpling, collapsing, burr, etc. Although excellent form accuracy can be obtained in the case of using a cutting apparatus exclusive to the honeycomb core, the cutting cost is inevitably increased in this case.
Under such a circumstances, disclosed in Japanese Patent Laid-Open No. 52-97484 was a method for cutting the honeycomb core with a high form accuracy, which comprises the steps of: filling the honeycomb core with such a material to be solidified as a thermoplastic resin, water, a paraffin, etc.; solidifying the material; cutting the honeycomb core and the solidified material; melting the solidified material; and removing the melt material from the honeycomb core. However, this method uses the liquid of a thermoplastic resin, etc. to be poor in workability. Further, the paraffin is often difficult to be removed from the honeycomb core after cutting.
A method using a polyethylene glycol having a melting point of 60 to 80xc2x0 C. as the material to be solidified also has been known. However, the polyethylene glycol is often melt by cutting heat and peeled off from the honeycomb core when this method is applied to cutting operation for a thin material or a high speed cutting operation. Further, the polyethylene glycol gives a lot of trouble when it is washed and removed from the honeycomb core after cutting, whereby cost increase is unavoidable in this method.
In a method disclosed in Japanese Patent Laid-Open No. 3-251329, the hollow tubular cells of the honeycomb core are filled with a rigid plastic foam block made of a polyurethane foam, etc., and the honeycomb core is cut together therewith. The rigid plastic foam block is shoved with a pressure into the hollow tubular cells and cut by the cell walls of the cells, whereby it is filled in the honeycomb core. However, this method is usable only in the case where the honeycomb core is made of such a material that has a sufficient strength, a metal, etc. Further, the rigid plastic foam block is not easy to remove from the honeycomb core.
An object of the present invention is to provide a method for easily cutting (machining) a honeycomb core with a reduced cost, excellent workability and high form accuracy, without using a cutting apparatus exclusive to the honeycomb core.
As a result of intensive research in view of the above object, the inventor has found that a honeycomb core is easily cut with a reduced cost, excellent workability and high form accuracy by filling or coating a hollow tubular cell of the honeycomb core with a gel and by solidifying the gel. The present invention has been accomplished by the finding.
Thus, a method of the present invention, which is for cutting a honeycomb core comprising a plurality of hollow tubular cells, comprises the steps of: filling or coating a hollow tubular cell of the honeycomb core with a resin composition that is in a gel state at an ordinary temperature; cooling the resin composition to a solid state; cutting the hollow tubular cell together with the resin composition in the solid state; allowing to stand or heating the resin composition to a gel state; and removing the resin composition in the gel state from the hollow tubular cell. The method of the present invention uses the resin composition in the gel state as the material to be solidified, thereby having an advantage in that the material is easy to handle and remove from the honeycomb core after cutting.
In the method for cutting a honeycomb core according to the present invention, the resin composition is particularly preferably changed from the gel state to the solid state at xe2x88x9220 to 0xc2x0 C. Further, the resin composition preferably comprises a water-absorbing resin and water.